Experiments Flashcards
(296 cards)
1
Q
Prep of a solution
A
-rinse pipette, burette, w/ d.i water, and with solutions/chemicals
(if using powder/crystals )-weigh out solute on weighed clock glass, subtract mass of clock glass
-put into (clean) beaker, rinsing clock glass w/ d.i. beaker to ensure all solute goes into it (rinsings)
-stir, dissolve
-use funnel, pour into volumetric flask, rinsing again as you do so using d.i. water
/
(If using a solution)-fill pipette with pipette filler up to mark with the bottom of meniscus on the mark
-transfer into volumetric flask using a funnel, then rinse funnel to ensure all of the solution goes into it
- fill up close to the mark with d.i. water, add final amount using dropper until bottom of meniscus on mark. Read at eye level.
- stopper, invert several times to ensure solute uniform through solution
2
Q
Iron tablet experiment - procedure for making up solution
A
- crush tablets with mortar and pestle
- washed into beaker
- stirred to dissolve
- transferred into flask using funnel
- rinsings added to flask
- add using dropper
- top up carefully until bottom of meniscus level with mark
- stopper, invert multiple times
3
Q
iron tablet - why use dilute sulfuric acid in making up solution
A
to prevent air oxidation of Fe²⁺ in solution to Fe³⁺
4
Q
iron tablet - why was more dilute sulfuric acid added before titration commenced?
A
to prevent formation of manganese(IV) (Mn⁺⁴) (brown precipitate) in solution
5
Q
iron tablet - how was end-point detected?
A
colourles to pink
6
Q
iron tablet - why nitric acid could not be used to provide acidic conditions for this reaction
A
nitric acid could not be used as it is a strong oxidising agent
7
Q
measuring the heat of neutralisation (of ethanoic acid by sodium hydroxide) in the school laboratory
A
- suitable container (polystyrene cup / calorimeter / glass vessel such as beaker) of known head capacity
- known vols & concs of acid and base
- measure initial temp, mix and note new (highest) temp
- calculate heat produced using mcdeltatheta
- calc for 1 mole H+ / calc heat of neutralisation
8
Q
why ethanoic acid and sulfuric acid would have diff heats of neutralisation
A
sulfuric acid: strong acid - dissociated, present as ions, energy not needed to dissociate)
ethanoic acid: weak acid (undissociated, slightly dissociated, present as molecules, energy needed to dissociate)
9
Q
water of crystallisation experiment - primary standard reagent which could have been used to standardise the HCL solution
A
anhydrous sodium carbonate
10
Q
water of crystallisation experiment - suitable indicator, colour change,
A
methyl orange
yellow to red
11
Q
water of crystallisation experiment - why not more than 1-2 drops of indicator should be used
A
methyl orange is a weak acid
12
Q
describe the correct procedure for rinsing the burette before filling it with the solution to deliver + describe filling it
A
rinse with deionised water
rinse with solution
- use funnel, pour in at top, take meniscus into account
- remove funnel
- ensure area below tap is filled
13
Q
why is it important to fill the part below the tap of the burette?
A
air will be displaced by solution
14
Q
describe procedure for weighing + making up solution from hydrated sodium carbonate crystals (for powders/crystals)
A
- weigh on clock glass using electronic balance
- transfer solution to beaker + rinse clock glass with d.i water using wash bottle to ensure all is transferred
- dissolve in d.i water
- transfer to volumetric flask using funnel + rinse with d.i water to ensure all is transferred
- add d.i water to up to near mark on flask
- add final amount using dropper, taking meniscus into account
- stopper, invert several times
15
Q
describe procedure for washing the pipette and using it to measure the solution
A
-rinse with d.i water, followed by solution
- fill up to mark with pipette filler taking meniscus into account
- transfer to flask with tip against side of flask to avoid splashing
16
Q
three precautions with burette that should be taken in order to ensure an accurate measurement
A
- vertical/read at eye level
- add dropwise using dropper near end-point
- rough titration first
17
Q
sodium carbonate crystals, is not a primary standard but anhydrous sodium carbonate (Na₂CO₃) may be used as a primary standard. Why is this the case?
A
- Na₂CO₃ is pure, stable, anhydrous (not hydrated), no water loss
- solution of exact concentration can be made, no need to standardise by titration, any opposite point for sodium carbonate crystals
18
Q
proceedure to measure out water from a beaker to a conical flask
A
- rinse pipette with d.i water and then the water sample
- use 25cm² pipette twice
- read mark at eye level, bottom of meniscus on mark
- touch tip against inside wall of conical flask, empty it out, do not blow out last drop from pipette
19
Q
describe how the melting point of the crude product/recystallised product of benzoic acid could have been measured
A
-know diagram
- sample on heating block
- thermometer in melting block
- block heated
- note temp range over which sample melts
20
Q
melting point benzoic acid experiment - two ways how you could conclude from melting points that the recrystallised product was purer than crude product
A
- higher melting point
- melting point closer closer to correct (in tables) value
- sharper (narrower range)
21
Q
one important use of benzoic acid or its salts
A
- food preservative
- disinfectant (antiseptic, fungicide)
- calibration
22
Q
describe the flame test
A
- dip platinum wire in HCl to clean, clean if it does not change flame colour
- dip in HCl
- dip in sample of salt, sticks to wire
- place salt in/over Bunsen flame
- note colour of flame observed
- if question specifies a salt, write the colour the flame should turn into
23
Q
flame test - the metals and their colours
A
Barium nitrate: yellow-green
Copper sulfate: blue-green
Lithium carbonate: deep red
Potassium sulfate: lilac
Sodium sulfate: yellow
Strontium nitrate: red
24
Q
flame test - why do metals give off a characteristic colour in a flame?
A
energy differences between energy levels in metal atoms vary from metal to metal. Using energy from flame, electrons move to higher energy levels then return to lower e levels, emitting light whos energies are equal to energy diff between higher e levels and lower e levels.
25
flame test - what procedure is used to avoid cross contamination?
Platinum wire: cleaned with concentrated HCL after each test
Wooden splint: diff splint used for each test
26
redox reactions of halogens - What is observed when chlorine gas is bubbled into an aqueous solution of sodium bromide? Explain your answer in terms of oxidation and reduction.
-solution turns red-brown
-bromide ions oxidised to bromide
Br⁻ --> Br₂
-chlorine reduced to chloride ions
Cl₂ --> Cl⁻
27
How do halogens react? + order of oxidising power
As oxidising agents, as they often react by taking an electron from another element.
F > Cl > Br > I > At
28
Why some halogens cant be used for the redox reaction
- Fluorine extremely poisonous
| - Astatine unstable + radioactive
29
Ethanoic acid in vinegar - measuring sample of vinegar and diluting it with d.i water
- use pipette previously rinsed with deionised water and then rinsed with the vinegar solution it will contain
- pipette: read at eye-level, bottom of meniscus on mark, don't shake out/blow out last drop
-transfer to volumetric flask previously rinsed with deionised water, fill with d.i water until bottom of meniscus on mark (dropper at end), stopper + invert number of times
30
Ethanoic acid in vinegar - indicator
phenolphtalein
31
Ethanoic acid in vinegar - colour change at end point
pink to colourless
32
Ethanoic acid in vinegar - why vingar is diluted
to avoid small titre which would reduce accuracy of experiment
reduces amount of vinegar and amount of sodium hydroxide solution needed in experiment
33
Ethanoic acid in vinegar - why is phenolphthalein used as the indicator
this is a weak acid/strong base titration and phenolphthalein changes colour in appropriate pH range
34
why rough titration carried out first
to find approx endpoint, enables subsequent titrations to be carried out more quickly + more accurately
35
why are three accurate titrations carried out
reduce experimental error by calculating average value
36
when doing titration calculations, remember
- dont use the first titration value given, as it is the rough titre unless stated that it is an accurate titre
- get the average of the accurate titres
37
starting with solution of anhydrous sodium carbonate, what two titrations are required to standardise a sodium hydroxide solution?
- anhydrous sod carbonate titrated with a strong acid (eg. HCl, sulfuric acid, nitric acid)
- acid titrated with sodium hydroxide solution
38
what compound in white wine is converted to ethanoic acid in vinegar? what type of chemical process converts this compound to ethanoic acid?
ethanol
oxidation
39
name piece of equipment that should be used to measure x solution during the titration
burette
40
precaution that should have been taken as end point of titration approached + how it would have contributed to accuracy of titration result
-add drop by drop
(so end point will be precisely/accurately detected
-swirl flask contents
(ensure thorough mixing of reactants)
41
water of crystalisation in sodium carbonate - indicator
methyl orange
42
water of crystalisation in sodium carbonate - colour change
yellow to pink/peach
43
in acid-base titrations, why preferable to use little of indicator as possible
indicator is a weak acid/weak base, excessive use will affect titre value
44
physical appearance of hydrated sodium carbonate
white crystalline solid
45
explain water of crystallisation
water present in definite proportions in crystalline compounds
46
identify a primary standard reagent which could have been used to standardise the HCl solution
anhydrous sodium carbonate (Na₂CO₃)
47
potassium manganate(VII)/ammonium iron(II) sulfate titration - why ammonium iron(II) sulfate suitable as primary standard
it is stable + available in a highly pure form
48
potassium manganate(VII)/ammonium irom(II) sulfate titration - indicator + observation at end point
- no indicator needed as manganate ions decolourised in reaction until end point
- pale pink colourless remains
49
why pipette + burette rinsed with di water followed by a little of solutions they were to contain
- di water washes out residual solutions in burette + pipette
- remove any residual water so as to avoid dilution of solutions when they are added
50
why conical flask rinsed with d.i only
di water washes out any residual solution in flask, but if it was washed out with solution it was to contain, traces of it would remain + there would not be a precisely known amount of solution in flask
51
why you wash down sides of conical flask with di water from a wash bottle
ensure all of solution transferred
52
why washing down with di water does not affect results
only di water added, no extra reactants introduced
53
procedure used during titrations to ensure accuracy of end point
- swirl flask while adding solution from burette
- rinse down walls of flask with di water at intervals
- add x dropwise as end point approached
- read burette at eye-level
- keep burette vertical
- carry out rough titration first
- use white tile to see colour changes in flask clearly
54
why are iron tablets sometimes medically prescribed?
- to prevent anaemia
| - for haemoglobin
55
iron in iron tablet - why potassium manganate(VII) must be standardised + why necessary to standardise immediately before use in titration
- not primary standard
- to find concentration
- unstable
- reacts with water
- affected by light
56
iron in iron tablet - reagent used for standardising potassium manganate (VII)
ammonium iron(II) sulfate
57
iron in iron tablet - how solution prepared from iron tablets
-tablets crushed + dissovled
-transferred with rinsings to volumetric flask using funnel
-bottom of meniscus on mark
-dropper
-stopper + invert
etc
58
why more than one titration carried out
reduce experimental error by getting mean of accurate titres
59
steps taken to minimise error prior to titration
- rinsed with di water
| - rinsed with solution etc
60
iodine/thiosulfate titration - how iodine, a non-polar substance of very low water solubility, is brought into aqueous solution
- reaction with potassium iodide (KI)
| - forms soluble potassium triiodide (KI₃)
61
iodine/thiosulfate titration - indicator
starch solution
62
iodine/thiosulfate titration - when indicator is added
-when colour in conical flask is light/pale yellow (close to end point)
63
iodine/thiosulfate titration - colour change at end point
blue-black to colourless
64
iodine/thiosulfate titration - why using distilled water instead of di water would ensure a more accurate result
-di water could contain non-ionic substances that could be oxidised/reduced
65
iodine/thiosulfate titration - what must be added to bring iodine into aqueous soln?
-source of iodide ions (eg. potassium iodide)
66
iodine/thiosulfate titration - sequence of colours observed in flask from start of titration until end point
- golden-brown colour
- light/pale yellow
- blue-black
- colourless
67
iodine/thiosulfate titration - why hydrated sodium thiosulfate not suitable as primary standard
- not stable
| - loses water of crystallisation readily
68
iodine/thiosulfate titration - why iodine solutions made up using potassium iodide solution
iodine is a non-polar substance of very low water solubility
69
iodine/thiosulfate titration - why starch solution has to be freshly prepared + why added close to end point
- it deteriorates quickly on standing
| - to give sharp end-point
70
hypochlorite in bleach - indicator + when its added
- starch solution
| - when colour of solution in flash fades to pale yellow colour
71
what should be rinsed with di water and then with the solution
Di water: pipette, burette, conical flask
Solution: pipette, burette
72
hypochlorite in bleach - colour change at end point
blue-black to colourless
73
hypochlorite in bleach - colour when potassium iodide and sulfuric acid reaacted with the diluted bleach
reddish-brown / brown / red
74
hypochlorite in bleach - why excess potassium iodide used
so all bleach (hypochlorite) has reacted and to keep the iodine in solution
75
why stand the conical flask on white tile during titrations
so that colour-change (End point) clearer/more easily seen
76
why use volumetric flask instead of graduated cylinder
volumetric flask is quite an accurate measuring vessel while g cylinder is not
77
hardness of a water sample - solution titrated against sample to measure hardness
EDTA (ethylenediaminetetraacetic acid)
78
hardness of a water sample - why boiling + filtering sample would lower ppm
-temporary hardness was removed, only permanent hardness remaining
79
full name of EDTA
ethylenediaminetetraacetic acid
80
hardness of a water sample - indicator + colour change at end point
- Eriochrome Black T
| - wine red to blue
81
hardness of a water sample - purpose of buffer solutions
-to stabilise the pH of a solution
82
hardness of a water sample - buffer required for titration
-buffer solution of pH 10
83
hardness of a water sample - problem if wrong buffer was used
- inaccurate end point
| - edta complexing with other ions
84
hardness of a water sample - operations involving the flask carried out as edta being added from burette during titration
- swirl flask o mix
- wash down sides with di water
- on white tile
85
hardness of a water sample - is the water having passed thru the deioniser suitable as di water in the lab?
- not suitable
- hardness remaining after passing thru deioniser
- deioniser needs to be replaced
86
hardness of a water sample - purpose of adding buffer solution
keep pH at around 10 / ensure sharp end-point
87
hardness of a water sample - reaction of adding dilute HCl to deposit found on insides of kettles from hard water
CaCO₃ + 2HCl --> CaCl₂ + H₂O + CO₂
88
dissolved oxygen by redox titration - why avoid trapping air bubbles each time stopped inserted into sample and when ussing dropper
would increase dissolved oxygen / oxygen concentration
89
dissolved oxygen by redox titration - solutions added to sample
- manganese(II) sulfate solution
- alkaline potassium iodide
-concentrated sulfuric acid
90
dissolved oxygen by redox titration - observation after adding sulfuric acid + mixing contents of bottle
brown solution
91
dissolved oxygen by redox titration - conclusion reached if a white precipitate observed instead of brown precipitate after first two additions of reagents to bottle filled with river water
extremely low oxygen in water
92
dissolved oxygen by redox titration - why is immediate determination of dissolved oxygen considered best practice
biochemical reactions occur / action of micro-organisms
93
dissolved oxygen by redox titration - why analyse sample of river water immediately?
- so oxygen content doesnt increase due to photosynthesis
| - so oxygen content doesnt change due to activity of organisms in water
94
dissolved oxygen by redox titration - in making additions to sample, why should solutions be concentrated?
-minimise change in oxygen dissolved in sample / so small volume (amount) supplies excess
95
dissolved oxygen by redox titration - how addition of conc solution of manganese(II) sulfate should be carried out
- additions made so water overflows from bottle
- make additions under level of the water
- using dropper
- do not bubble air (oxygen) into water in process
96
dissolved oxygen by redox titration - precautions when replacing stopper after each addition
-do not trap air (oxygen) bubbles
97
dissolved oxygen by redox titration - indicator + when it should be added + colour change at end point
- starch solution
- when solution is pale yellow
- blue black to colourless
98
dissolved oxygen by redox titration - why bottles shaken
help dissolved oxygen to react
99
dissolved oxygen by redox titration - why bottles are completely filled
prevent additional oxygen from air dissolving in water
100
dissolved oxygen by redox titration - why bottle stored in dark
prevent oxygen production by photosynthesis
101
why conical flask instead of beaker
allow easy mixing of contents by swirling
102
why funnel removed from burette after adding acid solution
so drops of solution from funnel will not fall into burette
103
why clamp burette vertically?
enable liquid level to be read correctly
104
how liquid level in burette adjusted to zero mark
- fill to below mark + add dropwise
| - bottom of meniscus on mark
105
why pipette filler used to fill pipette with solution
safety/hygiene
106
standardisation of HCl using standard soln of sodium carbonate - indicator + colour change at end point
methyl orange
yellow to red
107
test for carbonate anions
- add HCl solution
- effervescence, colourless gas evolved
- limewater test: becomes milky, CO₂ evolved
- Add magnesium sulfate, white precipitate formed
- heated, no change
108
test for hydrogencarbonate anions
- add HCl solution
- effervescence, colourless gas evolved
- limewater test: becomes milky, CO₂ evolved
- Add magnesium sulfate, no change
- heated, white precipitate appears
109
test for sulfate anions
- Add barium chloride, white precipitate formed
| - add HCl solution, no change
110
test for sulfite anions
- add barium chloride, white precipitate formed
| - add HCl solution, white precipitate disappears
111
test for nitrate anion
- add iron(II) sulfate
- nothing observed
- add concentrated sulfuric acid
- brown ring appears at boundary between liquid layers
112
ethyne - What is in each piece of equipment?
- water dropped onto calcium carbide (in reaction flask)
- acidified copper(II) sulfate solution in another tube
- water in water bath
113
ethyne - observation in reaction flask as water dropped onto calcium carbide
-turns milky / bubbling / effervescence (fizzing)
114
ethyne - why first few test tubes of gas collected were discarded
-contain air (nitrogen, oxygen, argon, carbon dioxide)
115
ethene, ethane, ethyne diagrams
know diagrams from notes
116
precautions when carrying out ethene experiment
- remove delivery tube from water before removing heat at end to avoid suckback into hot test-tube
- keep ethanol away from flame - ethanol flammable
- keep long hair tied back/wear gogles/wear gloves - avoid burns/contact with chemicals
117
ethene, ethyne experiments diagrams
know diagrams from notes
118
precautions when carrying out ethene experiment
- remove delivery tube from water before removing heat at end to avoid suckback into hot test-tube
- keep ethanol away from flame - ethanol flammable
- keep long hair tied back/wear gogles/wear gloves - avoid burns/contact with chemicals
- wear mask - avoid inhaling glass wool
119
reagent used to test gases for unsaturation
Bromine (Br₂) solution
120
reagent used to test gases for unsaturation
Bromine (Br₂) solution / Bromine water
Acidified potassium manganate(VII)
121
ethyne - appearance of calcium carbide
black/dark/grey
122
saturation test for gas
- bubble ethene/ethyne into bromine water
| - red (brown/orange) bromine solution decolourises
123
saturation test- ethene
-colour of bromine water changes from red to colourless
or
-purple colour changes to colourless (potassium manganate(VII)
124
saturation test - ethyne
-bromine water changes from red to colourless
or
--purple colour changes to colourless (potassium manganate(VII)
125
major use of ethene
-manufacture of polythene
126
major use of ethyne
- cutting metals
- welding metals
- make ethanal
127
major use of ethyne
- cutting metals
- welding metals
- make ethanal
128
organic product of adding bromine water to ethyne
dibromoethene or tetrabromoethane
129
describe how to test samples x and y for unsaturation
- Add bromine water
- decolourises if unsaturated
- no change in colour if saturated
130
ethene - what is in each piece of equipment?
- glass wool with ethanol in tube
| - aluminium oxide in tube over flame
131
ethene - what stage is suck-back likely to occur?
when heat is removed at the end
132
ethene - consequence of suck-back occurring
cold water sucked into test tube, causing test tube to crack
133
ethene - how to avoid suckback
-remove delivery tube from water before removing heat
134
ethene - colour of aluminium oxide
white powder/solid
135
ethene - type of reaction in preparation of ethene
elimination
136
Which evaporates more quickly, ethanal, ethanoic acid, or eugenol?
ethanal
137
ethanal - chemical test to confirm ethanal can be easily oxidised / test for ethanal
- Add Fehling's solution / Tollens' reagent
- heat gently
- Fehling's solution: red/brown precipitate formed. / Tollen's reagent: slver mirror formed
138
what happens when you add water to eugenol and shake it vigorously?
white emulsion formed
139
what happens when you add water to ethanoic acid?
colourless solution observed
140
observation after adding cyclohexane to eugenol
two layers
| -organic (cyclohexane) layer and aqueous layer
141
ways to test for ethanoic acid
- odour
- universal indicator paper
- magnesium strip
- anhydrous sodium carbonate
- ethanol with concentrated sulfuric acid
142
ethanoic acid - odour
vinegar odour
143
ethanoic acid - universal indicator paper
changes colour from green to red - solution is acidic
144
ethanoic acid - magnesium strip
effervescence - hydrogen gas generated
145
ethanoic acid - anhydrous sodium carbonate
effervescence - carbon dioxide gas generated
146
ethanoic acid - ethanol with concentrated sulfuric acid
sweet odour and oily droplets - ethyl ethanoate produced
147
colour change in oxidation of ethanol to ethanal
orange to green
148
test to see if organic product is an aldehyde
use ethanol tests
| fehling's solution/tollens' reagent
149
ethanoic acid - what is in what
- ethanol and water in tap funnel
| - sodium dichromate, water, sulfuric acid, boiling chips in flask that is in water bath over hot plate
150
ethanoic acid - precautions to avoid excessive heat production during addition experiment
- add in small quantities (dropwise)
- shake (stir) after each addition
- cool reaction vessel
151
ethanoic acid - colour change as ethanol was oxidised
orange to green
152
ethanoic acid - purpose of heating the reaction mixture under reflux after addition from tap funnel was complete
- to speed up reaction
- ensure complete oxidation
- heat without loss of vapour
153
ethanoic acid - how ethanoic acid product was isolated from reaction mixture
isolated by distillation
154
ethanoic acid - diagram of oxidising ethanol into ethanoic acid
2007 q2 diagram
155
ethanoic acid - observation of adding solid sodium carbonate to ethanoic acid
effervescence/fizzing/bubbling
156
free chlorine in swimming pool - reagents used to detect free chlorine + colour observed when it reacts with free chlorine
potassium iodide (KI) and ethanoic acid
orange
157
free chlorine in swimming pool - how a colorimeter could be used to estimate concentration of free chlorine in a sample
- prepare a number of standard solutions of reagent
- place in calorimeter + note colorimeter readings
- plot graph of concentration vs readings
- get concentration (ppm) of sample from graph using sample absorbance
158
free chlorine in swimming pool - problem if free chlorine level too low
-infection (disease)
159
free chlorine in swimming pool - problem if free chlorine level too high
- unpleasant smel
- eye/skin irritation
- taste impared
160
example of a free chlorine species in swimming pool water
Chlorine (Cl₂)
161
why is the level of free chlorine higher in swimming pool water than in drinking water
- to kill pathogens/harmful bacteria added by swimmers
- swimming pool water more contaminated
- higher level would b dangerous to drink/give bad taste to drinking water
162
describe how the concentration of suspended solids could be measured in a sample
- known volume of water sample through weighed filter paper
- dry filter paper
- find new mass of filter paper and residue (reweigh)
- calculate mass of reside by subtracting mass of filter paper
163
free chlorine - why potassium iodide used
it is readily oxidised to iodine by chlorine
164
free chlorine - why ethanoic acid used
to ensure all of the chlorine reacts and that all of the iodine formed dissolves
165
free chlorine - advantage of using colorimeter to determine chlorine
reading can be taken very quickly
166
determination of pH of a water sample
use pH mater or pH paper
167
determination of total dissolved solids using evaporation
- evaporate known volume of filtered water sample in weighed beaker
- reweigh afterwards
168
relative molecular mass of volatile liquid - diagram of apparatus
in notes
169
relative molecular mass of volatile liquid - example of a liquid suitable for use in this experiment
propanone (acetone) (56 degrees celsius)
170
relative molecular mass of volatile liquid - how mass of vapour determined
- weigh flask
- heat until all liquid gone (until vaporised), cool ,dry and reweigh
- mass is the difference
171
relative molecular mass of volatile liquid - how volume of vapour determined
-fill flask with water and empty into graduated cylinder
172
relative molecular mass of volatile liquid - why pressure of vapour is same as atmospheric pressure
-the pinhole means that vapour is exposed to the air
/
-vessel is open to atmosphere
173
relative molecular mass of volatile liquid - why is this method unsuitable for non-volatile liquids?
-they do not vaporise easily, boiling points are too high
174
relative molecular mass of volatile liquid - modern intrumental technique to measure relative molecular masses of liquids, solids, and gaseous substances
mass spectrometer
175
volatile liquid definition
easily vaporised/easily changed to gas
176
relative molecular mass of volatile liquid - proceedure of experiment
- diagram
- flask, sealed with foil with small hole, immersed so at least half is under water
- describe how mass, volume, and temp measured
177
relative molecular mass of volatile liquid - how temp of sample measured
-use thermometer to read temperature of water
178
relative molecular mass of volatile liquid - how may the pressure be measured?
barometer
179
re-crystallisation of benzoic acid + melting point - diagram
in notes
180
re-crystallisation of benzoic acid + melting point - describe a method to measure the melting point of benzoic acid
- sample on aluminium block shown in diagram, thermometer in melting block
- heat block slowly with bunsen burner
- note temperature range at which melting occurs (temperature measured on thermometer)
181
re-crystallisation of benzoic acid + melting point - The melting-point range of F is lower and broader than that of G. Which is the purer benzoic acid sample?
G.
F is less pure
182
re-crystallisation of benzoic acid + melting point - lab technique that could be used to purify impure benzoic acid
recrystallisation
183
re-crystallisation of benzoic acid + melting point - way of maximising yield of recrystallisation process
- use minimum amount of solvent (water)
- cool fully
- avoid crystallisation during hot filtration
184
re-crystallisation of benzoic acid + melting point - how would recrystallisation have affected the melting point range?
- melting point range sharper (narrowed, smaller)
- melting point raised
- melting point closer to correct (in tables) value
185
re-crystallisation of benzoic acid + melting point - solvent used for recrystallisation + why its suitable
- solvent: water
| - very soluble in hot but slightly less soluble in cold
186
what solids are collected in filtration paper?
insoluble solids
187
re-crystallisation of benzoic acid + melting point - where is the benzoic acid collected?
the second filtration after the crystallisation, which is after the hot filtration
188
re-crystallisation of benzoic acid + melting point - how could benzoic acid be separated from salt during the procedure?
- both soluble in hot water
| - benzoic acid less soluble in cold water so crystalises out of solution while NaCl remains in solution
189
re-crystallisation of benzoic acid + melting point - steps
1. dissolving
2. hot filtration
3. crystallisation
4. filtration
5. drying
190
re-crystallisation of benzoic acid + melting point - how benzoic acid was dried
- warm place
- dry in warm oven
- air drying (eg. leave on filter paper/on a radiator)
191
re-crystallisation of benzoic acid + melting point - how melting point of two diff samples differ
- impure lower melting point
- impure less sharp range
- recrystallised closer to correct value
- recrystallised sharper (narrower range)
192
use of benzoic acid
food preservative
| disinfectant
193
re-crystallisation of benzoic acid + melting point - why use minimum amount of hot water
to maximise yield / so crystals will form on cooling
194
re-crystallisation of benzoic acid + melting point - when insoluble impurities were removed + how
- filtration of hot solution / first filtration
| - remained on filter paper
195
re-crystallisation of benzoic acid + melting point - when soluble impurities removed + how
- filtration of recrystallised benzoic acid
| - stayed in solution
196
re-crystallisation of benzoic acid + melting point - how to ensure recrystallisation was complete
cool fully
197
heat of reaction of hydrochloric acid with sodium hydroxide - suitable material for reaction vessel to avoid heat loss to surroundings
polystyrene
styrofoam
plastic
cardboard
198
advantage of using burette instead of grad cylinger for measuring
more accurate
199
disadvantage of using burette instead of grad cylinder for measuring
slow addition
200
heat of reaction of hydrochloric acid with sodium hydroxide - ways of ensuring rise in temp measured as accurately as possible
sensitive thermometer used
avoid splashing
201
heat of reaction of hydrochloric acid with sodium hydroxide - hazards associated with solutions used
corrosive / burns skin / damages eyes
202
warning symbols
know how to draw warning symbols!
203
heat of reaction of hydrochloric acid with sodium hydroxide - experimental problem if 0.1M NaOh and 0.1M HCl used instead of 1.0M solns
very small temp rise
greater percentage error
204
heat of reaction of hydrochloric acid with sodium hydroxide - precaution when handling solutions
do not allow contact with skin, wear protective clothing (gloves, labcoat)
205
heat of reaction of hydrochloric acid with sodium hydroxide - how initial temp of reaction mixture could have been obtained if they were stored at diff temps
get average temps of two solutions
or
wait until both solutions at same temp
206
heat of reaction of hydrochloric acid with sodium hydroxide - three precautions taken to obtain accurate value for highest temp teached by reaction mixture
- sensitive thermometer
- add quickly
- add without splashing
- replace cover quickly
- stir constantly
207
heat of reaction of hydrochloric acid with sodium hydroxide - why use a polystyrene foam cup
its a good insulator/prevents heat loss
208
piece of equipment used in industry to measure heats of combustion
bomb calorimeter
209
rate of production of oxygen from hydrogen peroxide - diagram
diagram
210
decomposition - which run completed first and which had slower initial rate?
completed first: whatever stopped increasing in volume faster
slower initial rate: whatever stopped increasing in volume later
211
rate of production of oxygen from hydrogen peroxide - catalysis involved in reaction
surface adsorption
212
rate of production of oxygen from hydrogen peroxide - how catalyst could differ in diff runs
greater surface area / purer (for faster initial rate)
213
rate of production of oxygen from hydrogen peroxide - warning symbol put on hydrogen peroxide
circle with flames rising
214
rate of production of oxygen from hydrogen peroxide - why graph is steepest at beginning
greatest rate
215
rate of production of oxygen from hydrogen peroxide - finely powdered vs coarsely powdered - which would have greater average rate of reaction? + why
- finely powdered
| - greater activity/greater surface area available
216
rate of production of oxygen from hydrogen peroxide - change in graph if concentration of solution was lower
-rise less steep
217
benzoic acid from phenylmethanol - appearance of phenylmethanol at room temp
colourless / pale yellow
218
benzoic acid from phenylmethanol - colour change when phenylmethanol heated gently with potassium manganate(VII) solution
purple to dark brown
219
benzoic acid from phenylmethanol - substances added to allow separation of benzoic acid from other substances after oxidation was complete
Hydrochloric acid (HCl)
Sodium sulfite (Na₂SO₃)
220
benzoic acid from phenylmethanol - changes observed in reaction vessel after addition of two substances and as cooling occured
mixture decolourises
221
benzoic acid from phenylmethanol - changes in oxidation number of manganese during experiment
7 to 4 to 2
222
separation of a mix of indicators using chromatography - diagram
diagram (paper chromatography or thin-later chromatography)
223
define inmiscible liquids
do not mix
224
prep of soap - stages
- stage 1 - refluxing
- stage 2 - distillation
- stage 3 - washed into beaker containing brine
- stage 4 - filtration to isolate soap
225
prep of soap - purpose of refluxing in stage 1
- allow time for reaction / bring reaction to completion
| - without losing volatile material/without flask boiling dry
226
prep of soap - type of reaction in refluxing
saponification
227
prep of soap - substance removed by distilation
ethanol
228
prep of soap - function of brine
to precipitate the soap / soap insoluble in brine
229
prep of soap - why wash soap thoroughly in last stage
remove sodium hydroxide, which could burn skin when soap used
230
prep of soap - how to wash the soap
brine (salt solution) / ice-cold water
231
prep of soap - what is the co-product of the reaction? where was it located at the end of the process?
glycerol/glycerine **know how to draw molecule
in brine/filtrate
232
prep of soap - how a soap can dissolve both non-polar oils and ionic salts in sweat
C₁₇H₃₅ is non-polar and dissolves oils
-COO⁻Na⁺ attracted to salts in sweat
233
IUPAC name for glycerol
propane-1,2,3-triol
234
prep of soap - purpose of ethanol
solvent
235
prep of soap - diagrams
in notes
236
prep of soap - how ethanol removed after reflux stage
diagram of distillation
237
prep of soap - how soap isolated from other subtstances left in reaction mixture
- add in a little boiling water
- reaction mixture added to brine
- precipitated soap got by filtration
- wash with more brine
238
prep of soap - how soap purified + dried
purified: wash with brine
dried: warm place / oven / air dry
239
prep of soap - why remove ethanol after reflux
easier to isolate soap
soap contaminated with ethanol
240
prep of soap - location of excess sodium hydroxide
in filtrate/brine
241
observation of adding soap in di water
lather
242
observation in adding soap to mineral water from a limestone region
no lather
243
chemical difference between vegetable and animal fats
animal saturated
vegetable unsaturated
244
prep of soap - what should be added to reaction flask prior to reflux?
- lard
- sodium hydroxide
- ethanol
- anti-bumping agent
245
prep of soap - why a minimum of hot water used to dissolve residue from distillation
- maximise soap precipitation out
| - to minimise soap remaining dissolved
246
prep of soap - what is brine?
salt solution
247
prep of soap - how soap could be isolated from brine _
filter
248
prep of soap - precaution to ensure soap is free of sodium hydroxide
wash with brine
249
natural product you extract using steam distillation
clove oil (eugenol)
250
during reflux - what happened to liquid in flask during reflux?
hot vapour rose and was condensed (returned to flask)
251
refluxing - how did refluxing this mixture help bring reaction to completion?
allowed enough time to bring reaction to completion
heating without loss of reactants
252
extraction of clove oil from cloves - appearance of material collected during steam distillation
cloudy / milky liquid
| mixture of clove oil and water
253
extraction of clove oil from cloves - what distilled across along with the product?
water
254
extraction of clove oil from cloves - safety feature of steam distillation apparatus
- safety tube/steam tube: releases pressure/steam, preventing explosion
- air-tight seals: no steam escapes, preventing burns
255
substance you isolated by steam distillation + plant it was extracted from
clove oil from cloves
256
extraction of clove oil from cloves - function of safety tube (above flask)
- release of pressure
- prevents build up of steam
- avoids explosion
257
extraction of clove oil from cloves - technique to separate clove oil from water (liquid-liquid extraction of clove oil)
shake with suitable solvent (eg. cyclohexane)
258
use of clove oil
flavouring / seasoning / used in food
259
why clove oil cannot be distilled directly from cloves
clove oil contains component molecules whose boiling points are very high
260
effect on reaction rate of concentration and temp - method you could use to determine whether the same mass of x had been formed in each run
- cross under flask
- obscured
- when viewed through same depth of solution in each run
261
effect on reaction rate of concentration and temp - how to investigate effect of changing temp on reaction rate
- heat solutions using water baths/hot plate
- with fixed volumes and concetrations of sodium thiosulfate and HCl
- record reaction times
262
effect on reaction rate of concentration and temp - change observed in conical flask during reaction
- cloudiness
| - due to formation of sulfur
263
effect on reaction rate of concentration and temp - how observed changed used to obtain reaction times
- stand flask on cross
| - note time when cross becomes invisible
264
effect on reaction rate of concentration and temp - effect on experiment if lower molarity of solution used
-reaction slower
bc rate directly proportional to thiosulfate concentration
265
effect on reaction rate of concentration and temp - describe how you would measure the reaction time when hcl and sodium thiosulfate react
- place thiosulfate soln in a vessel over a cross on a white surface
- add HCl and start a stopwatch/timer
- note time when cross becomes invisible when viewed thru solution
266
effect on reaction rate of concentration and temp - describe how you would show rate of this reaction is directly proportional to conc of sodium thiosulfate solution
- repeat procedure for each solution
- find reciprocals of the times (1/t values) to get the rates
- plot 1/t against concentration
- plot of rate against concentration gives a straight line through the origin
267
effect on reaction rate of concentration and temp - precipitate produced in each flask
sulfur
268
effect on reaction rate of concentration and temp - why conc and volume of HCl kept constant
so only one variable is changed
269
effect on reaction rate of concentration and temp - would you expect reaction times to increase or decrease as temp increased?
decrease
reaction rate increases with temperature
270
effect on reaction rate of concentration and temp - why reciprocal of the time used as measure of initial rate of reaction
rate and time inversely related
rate ∝ 1/t
271
refluxing - glasssware used at the top
condenser
272
what is an emulsion?
oil droplets in water
273
clove oil - safety precaution when using separating funnel
work in fume cupboard
| avoid flame
274
clove oil - how clove oil isolated following liquid-liquid extraction
evaporate solvent/distil
275
benzoic acid - why you woildn't need to carry out a hot filtration (2018)
no insoluble impurities
276
benzoic acid - advantage of suction filtration over gravity filtration
faster / helps dry the crystals
277
benzoic acid - how you oculd verify recrystallised b acid was purer
-measure melting points of both samples
-purer: melting point closer to correct value
-impure: melting point ...
etc
278
heat of reaction - why stir
distribute heat evenly
279
heat of reaction - why temp begins to fall gradually later
heat loss to surroundings
280
heat of reaction - why use moderately concentrated solns instead of dilute solns
bigger temp rise recorded
less percentage error
281
heat of reaction - how you could get a more accurate result
- use insulation: stops heat loss to surroundings
| - use acids and bases with greater concs: greater temp rise
282
another organic compound that could be formed when ethanol is oxidised using acidified sodium dichromate
ethanoic acid / acetic acid
283
benzoic acid from phenylmethanol - explain colour change by reference to transition metal reagent used
MnO4^- changes to Mn^2+
284
Experiment: water hardness - rectifying splash of solution up side of conical flask + why
side of flask washed down with d.i. water
-doesn't affect concentration of reactants in flask as it contains no ions
285
Experiment: water hardness
solution added before titration proceeds + purpose
- pH 10 buffer solution
- added before titration proceeds
- keeps the pH at about 10, ensuring necessary conditions for effective operation of indicator are maintained
286
Experiment: water hardness - effect of boiling the water
the titre would be smaller as boiling removes temp hardness
287
iron tablet calculations - finding mass of iron in one tablet from concentration of iron in solution
- When you get the molarity, convert it from mol/L to mol/volume of soln (eg. 250 cm3),
- then use that value in n=m/mr to get the number of moles for 4 tablets
- then divide by 4 to get mass for one tablet
288
finding the number of moles of something
find the no of moles of the thing added from the burette, and the no of moles in the flask should be either the same or different (check mole ratio on balanced equation)
289
percentage yield questions
check question to see what they want you to use for percentage yield, eg "what is the percentage yield, in mass?" find mass then use those to get the % yield
290
Find no of moles when given grams of a crystal
Convert the mass to per litre first,
eg. "8.82g used, diluted to 250cm3 solution", this is 8.82g/250 cm3, however to use the n=m/mr formula, we must convert to per litre so multiply 8.82 by 4 first
291
water of crystallisation - x , getting a decimal
round up or down if you get a decimal or write it exactly as you get it
292
finding Mr (when you see moles on equation)
when finding Mr, ignore the mole in front of the chemical formula (eg. 3NaOH, just find Mr of NaOH, not 3NaOH)
293
heat of neutralisation - finding heat change when given temps of the acid and base, and highest temp recorded
- find average temp between acid and base (a + b/2)
- find temp change by doing highest temp - average temp of acid and base
- use heat formula
294
finding Mr - values to use
use the values given on the front of the paper
295
soap equation
learn off soap equation on sheet
296
describe how you would demonstrate the effects of particle size on rate
- mass of small particles equal mass of larger particles
- added to equal volumes of HCl of same conc
- note times to complete reactions
